For the last couple years, Gerard Butler’s been a Page Six fixture as the rumored beau of Jennifer Aniston and a poster boy for unremarkable romantic comedies that break hearts at the box office. Now, the “300” actor who made “This. Is. Sparta!” a rallying cry is out to prove that he’s something else entirely: a serious actor.

Butler has two projects this fall that will showcase a side of him rarely seen since he first started on the London stages more than a decade ago. This is not the whimsical Scottish flirt seen breezing his way through last year’s rom-bomb “The Bounty Hunter” or flexing through action duds like “Gamer.” This is a performer with chops.

“Machine Gun Preacher,” out Friday, is about as heavy as it gets (despite the title that makes it sound like a really cool Christian Xbox game or one of those fake trailers from “Grindhouse”). The movie is based on the true story of Sam Childers, a druggie ex-con from Pennsylvania who cleans up, finds Jesus and suddenly decides to open an orphanage in one of the most dangerous parts of war-torn Sudan. He becomes so obsessed with his mission that he begins to alienate and bankrupt his family (including wife Michelle Monaghan and daughter Madeline Carroll).

“With this movie, I was aware that I was going to come out the other end pretty beaten up and exhausted and that it was going to be a hell of a ride both physically and emotionally,” Butler tells The Post. “There was also the pressure of, ‘Are you going to completely screw this up?’ What if you start playing this guy and you realize you just don’t have the dialect — you don’t have the attitude? There are a lot of voices in my head telling me to turn the other way and forget I ever read it.”

He makes another unexpected turn in “Coriolanus,” a modern take on Shakespeare’s tragedy (but using the original dialogue) that co-stars and was directed by Ralph Fiennes. It opens Dec. 2, but is already earning Oscar buzz after recent festival screenings. Butler plays Tullus Aufidius, an enemy then unlikely ally of a general (Fiennes) unfairly banished from Rome by conspirators.
The weighty story line and a tricky dialogue are a long way from anything featuring Katherine Heigl.

“It’s about growing up as an actor, about wanting to prove yourself and also improve yourself,” Butler says. “Last year it felt like, ‘Gerry, if you want to cash in on your success, last year was the year to make a ton of money.’ I think I made like one-thirtieth of what I made the year before, making two independent art-house movies, and I’m glad it did, because it sustained me in another way, in my soul.”

Butler confirms that making these kinds of heavy dramas is more taxing on an actor.

“Yes, it’s more draining and ultimately more rewarding,” he says.

“The films that are easiest to do are perhaps the ones that you don’t get the most reward out of. You don’t come out of them with the best memories or remain the most proud of them. A couple of my movies where that’s not true are [2004’s] ‘Dear Frankie’ and [Guy Ritchie’s] ‘Rocknrolla.’ Those are movies that I didn’t find particularly hard to do, but I’m proud of how they came out.”
Anyone who doubts that this is a whole new Gerard Butler need only read a few of his recent interviews where he breaks down while talking about “Machine Gun Preacher.” (Thankfully, he kept it together for The Post. Comforting a movie star can be awkward.) Yep, the man who became a household name after violently vanquishing enemies with help from his CGI-abs in “300” now sheds tears. In public. On the record. And worst of all, does it while dining over . . . a salad.

Oh, the humanity.

According to the LA Times, Butler cried for a full two minutes during a recent lunch.

“This happened to me a lot when we were filming — I would just be overcome,” he said. “I feel every emotion. I haven’t talked much about this movie in a while, and I did the other day, and I just started crying. I cried for about five minutes.”

This new image doesn’t jibe with the macho, stubble-faced alpha male who cruises around California on a motorcycle and has reportedly dated enough hotties to field a lingerie football league team. At his 41st birthday party last year at New York’s The Darby, Australian comedian James Smith joked, “Gerard has been out so much he’s now just constantly on Page Six. Gerry is on Page Six so much they have to make it Page Seven.”

But when it comes to his acting work, the hunger for meatier roles recalls his early career when he was treading the boards in a UK stage version of “Trainspotting” and appearing in prestige costume drama “Mrs. Brown” opposite Judi Dench.

Those fans missing the old Gerry, however, shouldn’t shed any tears. Butler says he’s still game for a variety of projects.
“Does that mean that [more dramatic movies] are only what I’ll do from now on? Absolutely not,” he insists. “I’m going to keep changing it up. I still want to have fun and keep challenging myself.”

One future challenge could include a return to Spartaaaaaaa! (To be screamed only.) The director of the upcoming “300: Battle of Artemisia” hinted that Butler’s King Leonidas may make a cameo.